Ex-cricket star Imran Khan has taken an early lead as votes are counted in Pakistan's poll, but political rivals allege vote-rigging on a major scale.

Early unofficial results suggest his PTI party are in the lead, but it will need to form a coalition if it is unable to secure a simple majority.

Results are trickling in slowly, but election officials deny rigging saying there are simply technical problems.

The voting day saw bloodshed, with many killed in a blast at a polling station.

This historic election will mark only the second time that a civilian government has handed power to another after serving a full term in Pakistan.

With 42 percent of polling stations counted, the Election Commission of Pakistan had Khan's Pakistan Tehreek-i-Insaf (PTI) party leading in 113 of 272 contested National Assembly constituencies, according to Pakistan's Dawn Newspaper.